An Ultrawideband Diversity Antenna - CiteSeerX

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 57, NO. 6, JUNE 2009

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An Ultrawideband Diversity Antenna Terence S. P. See and Zhi Ning Chen, Fellow, IEEE

Abstract—A compact diversity antenna operating at an ultrawideband (UWB) frequency range of 3.1–5 GHz is proposed for use in portable devices. The antenna printed on a printed circuit board (PCB) slab consists of two notched triangular radiating elements with two feeding ports. A ground plane is etched on the reverse side of the PCB. The shape of the ground plane is optimized to improve the isolation between the ports as well as impedance matching. The simulated and measured results show that across the operating bandwidth, the antenna can achieve a broad impedance bandwidth 20 dB, avwith good performance in terms of isolation of erage gain of 2 dBi, and efficiency of 70%. The correlation between the radiation patterns shows consistent diversity performance across the UWB bandwidth. A method to derive the transfer function of the antenna has been proposed, which can be used to obtain the radiated pulses in the time domain. Furthermore, a parametric study is conducted to provide antenna engineers with useful information for designing and optimizing the antenna. Index Terms—Diversity, portable devices, ultrawideband (UWB) antennas.

I. INTRODUCTION

U

LTRAWIDEBAND (UWB) differs from conventional wireless technology as it uses an extremely wide band of an RF spectrum to transmit data. The Federal Communications Commission put in place several indoor and outdoor broadcast restrictions such that the maximum emission limits do not exwithin 3.1–10.6 ceed the levels, for instance GHz [1]. With the promising advantages of low-power, low cost, and high data rates within a limited range, the UWB is suitable for wireless personal area networks (WPAN) and other applications such as location, positing, and imaging systems. Another advantage of UWB is that it allows frequency reuse without causing any interference between nearby devices. The UWB technology enables a wide variety of WPAN applications. Examples include replacing the IEEE1394 cables between portable consumer devices with wireless connectivity and enabling high speed wireless universal serial bus (WUSB) connectivity for personal computers (PCs) and its peripherals such as printers, scanners, and external storage devices. A major limitation of the existing USB technology is the presence of the cables. With the high speed WUSB, devices such as printers, digital cameras, and scanners can be connected to the PC without cables. The WUSB promises the data transfer rate of 480 Mbps,

Manuscript received May 06, 2008; revised January 21, 2009. Current version published June 03, 2009. The authors are with the Institute for Infocomm Research, Singapore 138632, Singapore (e-mail: [email protected]; [email protected]). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2009.2019908

which is the same as the current wired USB 2.0 standard when the communication range is within 3 m. Beyond 3 m but within 10 m, the data transfer rate may be reduced, for instance, to 110 Mbps, although in time to come, the data rate will be able to reach 1 Gbps or more. The WUSB specifications will be based on the UWB radio efforts by the Multi-band OFDM Alliance (MBOA) and WiMedia Alliance, which both are industry associations that promote personal area range wireless connectivity and interoperability among multimedia devices in a networked environment. In the multi-band OFDM-based UWB systems, the spectrum can be divided into at most 15 sub-bands with each band having . a bandwidth of As in the case of conventional radio systems, it is vulnerable to multipaths. As such, the signals may combine destructively at a receiver, causing fading to occur. However, the reliability of the system can be improved with the use of diversity technology, which is achieved by using the information from the different branches available to the receiver so as to increase the signal-to-noise (S/N) ratio at the decoding stage. In an indoor environment, the random polarization and direction of the incoming signals make pattern (spatial) diversity a suitable technique [2]–[4]. In the pattern diversity scheme, the antennas with different beam patterns on each branch linked to the different channels are used. The multipath components are weighted differently at each channel, creating different interference patterns of the signal at each branch. Therefore, each channel will receive the transmitted signal with different strengths depending on the branch pattern and the propagation characteristics at that moment in time. The diversity antenna design for portable devices in consumer electronics, such as PCs, and mobile devices will be a challenging task due to the space constraint. It will be essential to maintain low mutual coupling when the antenna elements are placed in close proximity to each other and stable radiation performance across a broad operating bandwidth. The close proximity of the antennas not only makes the antenna system more compact, but also enhances the pattern directivity which is desirable for pattern diversity. However, due to the increased mutual coupling, the correlation between the channels will be increased and the system efficiency will be reduced. Several antenna types have been proposed for UWB applications [5]–[6]. However, the large size including the system ground planes makes them unsuitable to be used in the WUSB dongles. Also, the size of the diversity antennas designed for PCMCIA cards in laptop computers is large as the elements have to be sufficiently spaced apart in order to achieve good isolation [7]–[10]. In this paper, a compact UWB diversity antenna for portable devices is presented. As an example, the antenna is designed to cover an impedance bandwidth of 3.1–5 GHz (lower UWB

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Fig. 2. Measured and simulated input reflection coefficient and isolation.

substrate (Rogers 4003) has a relative dielectric constant of 3.38. The two radiators are separated 3 mm from each other and are symmetrically positioned with respect to the -axis. The radiators are excited via 50- microstrip lines of 1.86-mm width in and 135 configuration. Each radiator has a 1.5-mm a wide notch etched in a direction parallel to the feeding strip. The purpose of cutting the notches is to concentrate most of the current on the radiators instead of the system ground plane, especially at the lower operating frequencies, such that the effect of the ground plane and coaxial probe on the impedance matching and radiation can be greatly minimized [11]–[12]. A stub measuring 4 3 mm on the feeding strip near to the radiator is used for impedance matching. There is a gap of 1 mm between the ground plane on the reverse side of the PCB and the bottom side of the radiators. In addition, the mutual coupling between the two radiating elements can be reduced by having a central strip that extends vertically from the ground plane [7]. Fig. 1. Antenna geometry (a) front side and (b) back side.

III. IMPEDANCE, RADIATION, AND DIVERSITY PERFORMANCE A. Impedance Performance

band) and has a stable three-dimensional omni-directional radiation performance with high average gain across the operating bandwidth for wireless portable devices such as USB dongles. A method to calculate the transfer function of the antenna is proposed as well, from which the radiated pulses are obtained and analyzed. In addition to the broad operating bandwidth, the antenna is designed to achieve a high isolation between two ports across the operating bandwidth for diversity applications when the elements are placed close to each other. Moreover, a parametric study is carried out in order to study the influence of some of the important parameters such as the length of the notch, the position of the feed point, the separation between the radiators, and the width and length of the vertical strip on the ground plane.

II. ANTENNA DESIGN Fig. 1 shows the geometry of the proposed UWB diversity antenna and the Cartesian coordinate system. The antenna was printed on a 37 45 0.8-mm PCB slab, where other RF circuits can be integrated closely with the antenna. The dielectric

From the EM package IE3D that is based on the Method of Moments, the antenna shown in Fig. 1 was designed and optimized to operate in the lower UWB band of 3.1–5 GHz. In the simulations, the antenna was modeled on a finite-sized dielectric substrate. Fig. 2 shows the simulated and measured and isolation using the input reflection coefficient Agilent N5240A Vector Network Analyzer. From the figure, it can be seen that the antenna achieved an impedance bandwidth . Port 2 has the same the of 3.1–5 GHz for impedance response as that of Port 1. The isolation within the impedance bandwidth is greater than 20 dB. Furthermore, it is noted that the measured lower edge frequencies for both the impedance matching and isolation correspond closely to the simulated ones, which implies that the effect of the cable has been minimized. B. Radiation Performance The radiation characteristics of the antenna were investigated across the impedance bandwidth of 3.1–5 GHz. Fig. 3(a)–(c) shows the measured radiation patterns at 3.1, 4, and 5 GHz in the

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SEE AND CHEN: AN ULTRAWIDEBAND DIVERSITY ANTENNA

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Fig. 4. Measured (a) average gain and (b) peak gain for the total field when Port 1 was excited.

Fig. 3. Measured radiation patterns with Port 1 and Port 2 excitation in the (a) = plane, (b) = plane, (c) x-y plane.

= 45 225

= 135 315

= 90 ( )

three principal planes, namely the , 135 /315 , - planes. and In the measurements, Port 2 was terminated with a 50- load when Port 1 was excited, and vice versa. Comparing the patterns when Port 1 and Port 2 were separately excited, it can be observed that they cover complementary spatial regions symmetrically with respect to the - plane. Also, the patterns are relatively stable across the impedance bandwidth. For a small antenna to be used in mobile devices such as laptops, printers, DVD players, etc., in an indoor environment where the signal polarizations are random, the gain or/and radiation efficiency are vital performance indicators. As compared to the peak gain, the average gain of the total field is of greater interest for mobile devices. The average gain at a particular frequency is defined as

(1) where, stands for the average gain of the total field, namely the sum of the and components along a specific is the gain measured at a parcut or orientation; or along a specific cut; and is the ticular orientation . total number of measured

In order to calculate the average gain, the gain for both the and components at a certain point along a specific cut is measured, and the gain for the total field is then calculated. With this process repeated times, the average gain for the total field can be obtained using (1). Fig. 4(a) and (b) show the average gain and peak gain of the total field at the principal planes, respectively. In this study, only the radiation in one half-space will be of interest. For the plane when Port 1 was excited and the plane when Port 2 was excited, the average gain is – computed for the right half-space region (i.e., ), whereas for the plane when Port 2 was plane when Port 1 was excited, excited and the is considthe left half-space region from ered. In the - plane, the average gain for the total field is calculated for the left half-space region (i.e., – – ) when Port 1 was excited and for the right half-space region when Port 2 was excited. The value of used in the calculation of the average gain is 91. The comparison in Fig. 4(a) and (b) shows that the measured peak gain is 2–3 dB higher than average gain over the bandwidth. This suggests that the radiation in such three planes is directional. The variation of the average gain is a good indicator of the stability of the radiation patterns within the bandwidth. From the figure, it can be observed that the average gain is greater than across the bandwidth. Also, it is noted that the variation in the average gain is within 3 dB at the three principal planes. Due to the symmetrical structure, the average and peak gain when Port 2 was excited will be the same as that in Port 1. The 3-dimensional radiation patterns for the gain of total field were measured at frequencies of 3.1, 4, and 5 GHz when Port


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Fig. 6. Measured and simulated antenna efficiency.

Port 1 was being excited. The nearly isotropic radiation characteristic is conducive to the application of the antenna in portable devices. Fig. 6 plots the simulated and measured antenna efficiency from 3–5 GHz, which was calculated from the gain and the directivity of the 3-dimensional radiation patterns. It can be seen that the efficiency is at least 70% across the bandwidth. On average, the antenna has a measured efficiency of about 80% with a peak efficiency of 93% at 4.75 GHz. The lower measured efficiency as compared to the simulation is due to the additional losses in the connectors and cables. Fig. 7(a) shows the current distributions on the antenna at 3, 4, and 5 GHz when the left radiator is excited at Port 1. It can be seen that most of the current is concentrated around the notch and the central vertical strip instead of the ground plane, especially at the lower frequency of 3 GHz [11], [12]. As such, the size of the radiator can be reduced and yet maintain the lower edge operating frequency at 3 GHz. In addition, since there is little current on the ground plane around the right radiator, mutual coupling between the two antenna elements is significantly reduced. The current distributions at 3 GHz for the different of the ground plane are also illustrated in Fig. 7(b). lengths It can be seen that the current is mainly concentrated around the notch at 3 GHz for the different lengths of the ground plane. This suggests that good isolation can be maintained with little variation in the impedance matching at the lower operating frequency. In this way, the radiator can be optimized for a particular ground plane and used on another ground plane of a different length depending on the application requirements. In Fig. 7(a), the higher current at 5 GHz on the radiator connected to Port 2 as compared to 4 GHz is consistent with the higher mutual coupling from Fig. 2. C. Diversity Performance Fig. 5. Measured three-dimensional gain for the total field at (a) 3.1 GHz, (b) 4 GHz, (c) 5 GHz.

1 was excited, by using the Orbit-MiDAS system as shown in Fig. 5 [13]. It can be seen that the radiation is almost omnidirectional in the entire three-dimensional space, which is unlike a typical monopole/dipole antenna because the and -components of the electric currents on the antenna are both strong. The -axis direction as only radiation is slightly weaker along the

Fading is a destructive interference due to multipath, which can be mitigated by using pattern diversity with multiple antennas. In this way, a significant reduction in fading can be achieved. As a result of the pattern diversity, the two rays from different directions will be experiencing different gain from the two antenna elements. This will reduce the likelihood that simultaneous fading will occur at both the elements at the same frequency. The envelope correlation coefficient is a figure-of-merit which can be used to gauge the diversity performance of the



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Fig. 8. Measured envelope correlation.

IV. TIME-DOMAIN PERFORMANCE In this section, a methodology to obtain the radiated pulses for the diversity antenna is presented. Generally, for a given source pulse, the radiated pulses can be computed if the transfer function of the antenna under test (AUT) is known. It was proposed that by using a pair of identical antennas, the transfer function can be obtained by using the ABCD and -parameters [15]. However, small antennas are usually less directive and have lower gain, thereby affecting the transmission performance. It will be desirable if the gain of the transmit or receive antenna is for a partichigh in order to achieve a good transmission or ular distance. As such, it will be useful if the transfer function of the AUT can be obtained when a pair of different antennas is used. In this study, in order to calculate the radiated pulses, the AUT is the transmit antenna. The receive antenna is a standard gain horn antenna (SGA). In general, the antenna system transfer can be expressed as [15] function,

Fig. 7. Current distributions at (a) 3, 4, and 5 GHz when l w and (b) at 3 GHz when w .

= 37 mm

= 37 mm

= 26 5 mm and :

antenna. It measures the degree of similarity between the beam , the two patterns are patterns of two antennas. When identical. This implies that the signal received by Port 1 will be the same as that in Port 2, . any fading will be experienced by both the two ports simultaneously. On the other hand, when , there will be with no overlap between the patterns of the two antennas. In this case, the incoming signal from any direction will only be received by at most only one of the two antenna elements. Although the fading might still occur depending on the direction of the incoming signal, it will be more robust than using a single omnidirectional antenna. The low correlation may imply that there is little overlapping between the two beam patterns. The correlation coefficient shown in Fig. 8 can be calculated using the -parameters as shown in (2) [14]. From the figure, the measured envelope correlation coefficient is lower than -25 dB across the UWB band of 3.1–5 GHz

(3) and are the transfer functions of the transmit where and receive antennas. The impedances and are the reference source and load impedances of Port 1 and 2, respecand are the input impedances of the transmit tively; and receive antennas, respectively; is the distance between the transmit and receive antennas (which ensures the transmit and receive antennas are in the far-field zone of each other.); is and are the unit vecthe free space wave number, and tors that indicate the polarization direction of the transmit and receive antennas, respectively. and with respect to the source and load Normalizing impedances, respectively,

(2)


(4)

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where and represent the normalized input impedances of the transmit and receive antennas, respectively. The normalized input impedances can be expressed in terms of the -parameters,

(5) Taking the ratio of the system transfer functions, where is the system transfer function with the AUT as the transmit antenna and the SGA as a receive antenna, is the system transfer function when and the SGA is used for both the transmit and receive antennas. Since

(6) where is the complex transmission coefficient which takes into account the polarization matching factor, if

(7)

The transfer function be calculated as [15]

of the transmit SGA can

(8) The radiated pulse can be then obtained by multiplying the spectrum of the source pulse that is defined in (9) with the transfer function of the AUT and the distance factor, , before taking the inverse Fourier transform. The normalized source pulse is plotted in Fig. 9(a). Using (8), the radiated pulses , , at were calculated and shown in Fig. 9. and These points were selected which correspond to the strong radiated fields when Port 1 was excited according to Fig. 3. In this ps study, as an example, a Gaussian monocycle with was selected as the source pulse with the peak of its spectrum located at 4 GHz

(9)

Fig. 9. (a) Normalized source pulse. Radiated pulses when Port 1 is excited = , ; (c) = , ; and (d) for (b) , .

= 90

= 45 225 = 180

= 090

= 135 315

= 90

In order to assess the ability of a coherent receiver to detect the received signal, a parameter known as fidelity was calculated by using a template to correlate with the source pulse [16]. The distortion of the radiated pulses against the source pulse can be calculated by using choosing the template to be the source pulse. Table I shows the fidelity calculated from the radiated pulses in Fig. 9 when the template is the source pulse. Also, by



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TABLE I FIDELITY OF RADIATED PULSES WITH VARYING TEMPLATES

selecting the optimal pulse parameter for the Gaussian monocycle, maximum fidelity can be obtained. V. PARAMETRIC STUDY A parametric study was carried out to investigate the effects of the important parameters on the impedance matching and isolation. This will be helpful for antenna designers to optimize the antenna during design. The effects of varying the separation (d) between the two radiators, the width of the vertical strip on the ground plane, length of the notch on the radiator, on the ground plane, position of length of the vertical strip as well as the length and width of the feed point the ground plane are studied. In the simulations, the values of the parameters are the same as that shown in Fig. 1, except for the parameter under investigation. As observed from Fig. 10(a), when the distance (d) between the radiators is increased, there is an upward shift in the lower edge frequency. This is due to an increase in the real part of the input impedance and a corresponding decrease in the imaginary part. The isolation is mainly affected at the lower and upper edges of the pass-band. The width of the vertical strip on the ground plane has a significant effect on the lower edge frequency as shown in Fig. 10(b). The real part of the input impedance is decreased and the imaginary part increased with an increase in the width. The lower edge frequency for the impedance matching and isolation experiences an upward shift with an increase in the width of the strip. The introduction of the notch on the radiators has a significant influence on the impedance matching and isolation at the lower edge frequency as shown in Fig. 10(c) [11]. With the notch, the size of the antenna can be reduced. This can also be seen from the current distributions in Fig. 7, where majority of the current is predominantly concentrated near the notch region at the lower operating frequency of 3 GHz. Generally, an increase in the notch length (or decrease ) decreases the lower edge frequency by increasing the real part of the input impedance and reducing the imaginary part. can be used to control the The position of the feed point impedance matching of the pass-band from 3.5 to 4.5 GHz as observed from Fig. 10(d). The upper edge frequency can be increased with an increase in the point with a decrease in the reactance. However, as the two resonances are spaced further apart, the matching at the center frequency will be deteriorated. The isolation is relatively insensitive to the position of the feed

point. The vertical strip on the ground plane can be used to reduce the mutual coupling as well as for impedance matching. of the strip is From Fig. 10(e) and (f), when the length decreased, the mutual coupling increases significantly and the impedance matching is degraded, especially when gets lower than 25 mm. The overall size of the antenna is dependent on the length and width of the ground plane. As shown in Fig. 10(g), an increase in the width of the ground plane will decrease the upper resonance such that the matching and isolation at the center frequency are improved. From Fig. 10(h), it can be seen that when the length of the ground plane is varied, good impedance matching and high isolation can still be achieved. This suggests that the ground plane effect of the proposed antenna is minimized. The length of the ground plane will be dependent on the applications. By reducing the effect of the ground plane, the radiator which has been optimized for a particular ground plane size can also be used on another ground plane of a different size without the need to re-optimize the radiator. VI. CONCLUSION A printed compact ultrawideband diversity antenna has been presented for portable devices. The achieved impedance bandof the proposed antenna covers the width for range of 3.1–5 GHz. The simulated and measured results have shown that the antenna is capable of having good isolation of and providing the pattern diversity to combat the multi-path fading across the operating bandwidth. The key of this design is that the ground plane effect has been reduced by notching the radiators so that the mutual coupling through the common ground plane has been greatly suppressed. The orthogonal configuration has ensured the reduction of mutual coupling. Also, it was observed from the measurements that the average gain for the total fields is also stable across the bandwidth. Also, the radiation patterns of the antenna are nearly isotropic and the radiation efficiency is at least 70%. The correlation coefficient was also introduced to assess the overall diversity performance of the antenna. The proposed antenna was able to achieve the stable correlation coefficient across the bandwidth along a certain planes. A method to calculate the antenna transfer function was proposed by using a pair of different antennas, which can be used to compute the radiated pulses. The parametric study was conducted to provide antenna engineers with useful information about the design and optimization of the proposed UWB antenna.


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[2] E. Jones, “Measured angle-diversity performance of the wire-grid lens antenna,” IEEE Trans. Antennas Propag., pp. 484–484, May 1967. [3] E. W. Allen, “Angle diversity test using a single aperture dual beam antenna,” in Proc. IEEE ICC’88, Jun. 1988, vol. 3, pp. 1626–1626. [4] R. G. Vaughan, “Beam spacing for angle diversity,” in Proc. IEEE GLOBECOM’98, Nov. 1998, vol. 2, pp. 928–928. [5] M. J. Ammann, “Square planar monopole antenna,” in Proc. Inst. Elect. Eng. Nat. Conf. on Antennas Propag., 1999, vol. 1, pp. 37–37. [6] S. Y. Suh, W. L. Stutzman, and W. A. Davis, “A new ultrawideband printed monopole antenna: The planar inverted cone antenna (PICA),” IEEE Trans. Antennas Propag., vol. 52, no. 5, pp. 1361–1364, 2004. [7] K. L. Wong, S. W. Su, and Y. L. Kuo, “A printed ultra-wideband diversity monopole antenna,” Microw. Opt Technol. Lett., vol. 38, no. 4, pp. 257–259, 2002. [8] G. M. Chi, B. H. Li, and D. S. Qi, “Dual-band printed diversity antenna for 2.4/5.2 GHz WLAN application,” Microw. Opt. Technol. Lett., vol. 45, no. 6, pp. 561–563, 2005. [9] L. Liu, H. P. Zhao, T. S. P. See, and Z. N. Chen, “A printed ultrawideband diversity antenna,” in Proc. Int. Conf. for Ultra-Wideband, Sep. 2006, pp. 351–356. [10] H. P. Zhao, L. Liu, T. S. P. See, Z. N. Chen, and M. J. Ammann, “A printed UWB diversity antenna,” presented at the Int. Symp. Antennas Propag., Nov. 2006. [11] Z. N. Chen, T. S. P. See, and X. M. Qing, “Small printed ultrawideband antenna with reduced ground plane effect,” IEEE Trans. Antennas Propag., vol. 55, no. 2, pp. 383–388, Feb. 2007. [12] Z. N. Chen, Antennas for Portable Devices. New York: Wiley, 2007, ch. 7. [13] Microwave Data Acquisition and Analysis Antenna Measurement System, Version 4 2004, Doc. No. MAL-3000-M4Aq. [14] S. Blanch, J. Romeu, and I. Corbella, “Exact representation of antenna system diversity performance from input parameter description,” Electron. Lett., vol. 39, no. 9, pp. 705–707, May 2003. [15] X. M. Qing, Z. N. Chen, and M. Y. W. Chia, “Characterization of ultrawideband antennas using transfer functions,” Radio Sci., vol. 41, no. RS1002, 2006. [16] Z. N. Chen, X. H. Wu, H. F. Li, N. Yang, and M. Y. W. Chia, “Considerations for source pulses and antennas in UWB radio systems,” IEEE Trans. Antennas Propag., vol. 52, no. 7, pp. 1739–1748, Jul. 2004.

Terence S. P. See received the B.Eng. and M.Eng. degrees in electrical engineering from the National University of Singapore, in 2002 and 2004, respectively. In 2004, he joined the Institute for Infocomm Research, Singapore, where he is currently holding the position of Senior Research Engineer in the Antenna Lab, RF and Optical Systems Department. His main research interests include antenna design and theory, particularly in small and broadband antennas and arrays, diversity antennas, antennas for portable devices, and antennas for on-body communications.

Fig. 10. Effects of varying the (a) d, (b) w , (c) l , (d) m, (e),( f) l , (g) w , (h) l on the impedance matching and isolation.

REFERENCES [1] First Report and Order in the Matter of Revision of Part 15 of the Commission’s Rules Regarding Ultra-Wideband Transmission Systems FCC, 2002, ET-Docket 98-153.

Zhi Ning Chen (M’99–SM’05–F’08) received the B.Eng., M.Eng., Ph.D., and Do.E. degrees from the Institute of Communications Engineering, China, and the University of Tsukuba, Tsukuba, Japan, all in electrical engineering. Since 1988, he has worked in Institute for Communications Engineering, Southeast University, City University of Hong Kong, China with teaching and research appointments. During 1997 to 1999, he conducted his research in University of Tsukuba, Japan, as a Research Fellow awarded by Japan Society for Promotion of Science (JSPS). In 2001 and 2004, he visited the University of Tsukuba, Japan again sponsored by Invitation Fellowship Program (senior level) of JSPS. In 2004, he worked in Thomas J. Watson Research Center, International Business Machines Corporation (IBM), Yorktown, as an Academic Visitor. In 1999, he joined Institute for Infocomm Research as Member of Technical Staff (MTS) and then promoted Principal MTS. He is now working as Principal Scientist and Department Head for RF & Optical. He is concurrently holding Adjunct/Guest Professor Appointments in National University of Singapore and Nanyang Technologies University, Nanjing University, Southeast



University, and Shanghai Jiao Tong University. He has been appointed Technical Advisor in Compex since 2005. His research areas cover applied electromagnetics and antenna theory and design wireless communication and imaging systems. In particular, he is interested in the R&D of small and broadband antennas and arrays for WLAN, WiMAX, WPAN, RFID, MIMO, ultrawideband (UWB), millimeter wave (mmW), submmW, THz, and implanted systems. He has authored and coauthored over 230 technical papers and the book Broadband Planar Antennas (Wiley, 2005), coedited UWB Communications (Wiley, 2006), and edited Antennas for Portable devices (Wiley, 2007). In addition, he has contributed multiple chapters to three books about antenna designs. He has

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been granted five patents and filed eleven patent applications. Some of them have been licensed to industry for productions. Dr. Chen is a Fellow of IEEE and IEEE Antennas and Propagation Society Distinguished Lecturer (2008–2010). He founded the IEEE International Workshop on Antenna Technology (iWAT), one of most important international antenna event, and as General Chair, organized the IEEE iWAT: Small Antennas and Novel Metamaterials, 2005, Singapore. He is Chairing the iWAT Steering Committee and managing future iWAT. He has played the important roles in many international events as chairs for Technical Program Committee and International Advisory Committee as well as keynote/invited speakers.
